This invention relates to rechargeable sealed lead-acid batteries of the absorbed electrolyte type, in which oxygen generated on overcharge is consumed internally within the battery.
The first sealed recombining lead-acid battery of high discharge capacity whose useful life was not limited by water loss on overcharge was revealed in the disclosure of McClelland et al. U.S. Pat. No. 3,862,861. Applicants' assignee pioneered the development and commercialization of the invention of U.S. Pat. No. 3,862,861 by introducing a line of spirally wound cells characterized by a highly absorptive separator and unique electrolyte distribution. Subsequently, monobloc multicell parallel plate batteries employing these principles were introduced, the cells of which were sealed off from one another to preclude intercell migration of electrolyte and/or gases. Because the electrolyte fill level and intracell compression between plates and separators of these batteries can vary significantly from cell to cell, the respective voltages and capacities of the cells also vary, as do the gas recombination rates as well. These variations in cell characteristics compromise battery performance and life.
With respect to sealed alkaline and certain sealed acid systems in which the amount of electrolyte is limited to that necessary for ion transfer between the electrodes as taught in Abramson U.S. Pat. No. 3,170,819 (however, quite unlike the lead-acid system and more particularly the unique electrolyte distribution taught in the aforementioned U.S. Pat. No. 3,862,861) there is suggested the use of a manifolding arrangement between the cells in a multicell battery to overcome problems due to unequal capacities of individual cells. It is taught that oxygen liberated from weaker cells which are driven in reverse during a complete discharge combines with the negative active material of stronger cells which are not yet polarized, thereby tending to equalize the state of charge of the cells of the battery and improve its performance. This patent applies to electrochemical systems employing an invariant electrolyte, the capacity of which is not determined by the amount of electrolyte present. In the alkaline system, for instance, hydroxyl ions are generated during a charge or discharge at approximately the same rate at one electrode as they are consumed at the opposite electrode. In contrast, the sulfate ion quantity and concentration in the electrolyte in the lead-acid system, which varies according to the state of charge, serves as a yardstick from which the discharge capacity of the battery is determined.
It is a primary object of the invention to provide a multicell sealed lead-acid battery of the recombination type having the electrolyte fully absorbed within the plates and separators, in which the cells intercommunicate by gas redistribution so that imbalance in electrolyte fill levels among the cells are compensated for upon overcharge of the battery. It is a further object to provide a battery of the aforementioned type which can be discharged, charged (and overcharged), and stored in any indiscriminate attitude without intercell electrolyte migration or other adverse effect. It is still a further object in another aspect to provide the battery of the recombination type with cell assemblies consisting of plates and separators held under a common stacking pressure throughout the battery to optimize electrolyte distribution and to promote uniform utilization of the materials of the battery upon discharge, charge and storage. Other objects will become evident upon a reading of the following specification and claims.
In addition to the aforementioned prior art, the following references are also exemplary of the prior art: U.S. Pat. No. 2,742,520 (Pucher et al.); and U.S. Pat. No. 3,530,001 (Harivel).